It has been known for some time that waste waters containing contaminants such as impurities discharged from gas works, coke ovens, generator stations, oil refineries and certain areas of the chemical industry, particularly where such waste waters include phenols and other organic contaminants, can be treated with ozone in order to decompose and eliminate such contaminants. Thus, as reported in Polish Pat. No. 56,775 of May 15, 1969, ozone has been used to purify water from coke ovens containing one to two grams of phenols per liter employing 1.6 to 2 grams of ozone per each gram of oxidized phenol in a continuous oxidation process. In a process involving the ozonization of ammonia water containing 150 to 270 mg/l of phenols, 1.2 to 1.5 g of ozone per g of oxidized phenol were consumed.
As reported in said Polish patent the cost of purifying one cubic meter of phenolic effluent by the continuous method using ozone has proved too expensive and uneconomical for industrial use. The Polish patent, therefore, suggests a continuous process in which waste waters are treated with ozone in a froth phase. This process involves the use of a scrubber packed with Rashig rings, slag and/or oxides of silver, copper, aluminum, zinc, magnesium, tin, lead, iron, or manganese as catalysts. The air or oxygen containing 1 to 2% ozone is blown countercurrent to the waste water. The flow rate of the waste water and air is adjusted in such a way that a froth phase exists in the middle of the scrubber, the liquid being in the lower level and the gas phase in the upper level. Due to the large surface interface, the ozone initiates the oxidation process of the phenols which is finally performed by means of oxygen.